Well, here's where I'm at so far:
There's a guy who famously reverse engineered YouTube's private API years ago and implemented a client in C#
I don't really know C#, but I learned enough of it to make synchronous equivalents of all of his async functions, which makes it compatible with the
pythonnet C#-to-Python interface:
I then wrote a REST API in Python WSGI around that:
This will run on a linux box on your local LAN and act as a YouTube API and realtime video transcoder.
So at this point I just need to write a Cocoa desktop app which acts as a client for the API and launches MPlayer (or maybe have the API stream RTSP to QuickTime).
I have about four years of Objective-C experience, but that was back before I switched to Swift in 2015, so I'm having to dust off some cobwebs there. Also, AppKit is quite a bit different than UIKit (I'm an iPhone developer, not a Mac developer), so there's definitely a learning curve.
However, I have started watching the WWDC videos from the 2000 to 2004 era:
and I've found that though Apple has taken all of their old ADC Reference Library sample code offline, they are still available via the old Apple Developer Connection DVD sets:
I uploaded the last copy of the ADC library which was Leopard-specific to github so that the source of the sample projects is browseable:
and made the HTML browseable via github.io at:
So I think I'll probably have something working in maybe four more weekends.